Conventionally, in systems, known as processing systems, such as chemical plants, electric power plants, and the like, control is through instruments that are driven through the pressure of a fluid such as, for example, air, instead of electricity, in order to prevent explosions. With pressurized fluid supplied to the instruments, if the pressure is too high, may cause malfunctions or faults, and thus the pressure is reduced through a pressure-reducing valve. One type of pressure-reducing valve is a diaphragm-type pressure-reducing valve (referencing, for example, Japanese Unexamined Patent Application Publication No. 2000-120896).
A diaphragm-type pressure-reducing valve is provided with a first ON/OFF valve that connects or isolates an input chamber and an output chamber, and a second ON/OFF valve that connects or isolates the output chamber and an exhaust chamber, where this first ON/OFF valve and second ON/OFF valve carry out opposite operations alternatingly. Through this, the pressurized fluid that enters into the output chamber from the input chamber is depressurized, and the pressurized fluid that enters into the exhaust chamber passes through an exhaust hole to be expelled to the outside of the pressure-reducing valve.
In this diaphragm-type pressure-reducing valve, the first ON/OFF valve is structured from a supply air port that is formed as a through hole for connecting the input chamber and the output chamber, and a first valve unit that opens and closes an opening portion of the input chamber side of the supply air support, where the second ON/OFF valve is structured from an exhaust port that is formed as a through hole for connecting the output chamber and the exhaust chamber, and a second valve unit for opening/closing the opening portion at the output chamber side of the exhaust port.
The supply air port that structures the first ON/OFF valve is structured in a supply air port member that is provided in a partitioning wall that divides the input chamber and the output chamber, and the exhaust port that structures the second ON/OFF valve is structured in an exhaust port member that is bonded to a diaphragm that separates the output chamber and the exhaust chamber. Moreover, the first valve unit that structures the first ON/OFF valve and the second valve unit that structures the second ON/OFF valve are structured at one end and the other end of a poppet valve.
One example of a conventional diaphragm-type pressure-reducing valve is illustrated in FIG. 7. An enlarged view of the critical portions in FIG. 7 is presented in FIG. 8. In FIG. 7 and FIG. 8, 101 is an input chamber, 102 is an output chamber, 103 is an exhaust chamber, 104 is a partitioning wall for separating the input chamber 101 and the output chamber 102, 105 is a diaphragm for separating the output chamber 102 and the exhaust chamber 103, 106 is a supply air port member that is provided in the partitioning wall 104, 107 is an exhaust port member that is bonded to the diaphragm 105, and 108 is a poppet valve.
A supply air port 106a is formed as a through hole in the supply air port member 106, for connecting the input chamber 101 and the output chamber 102, and an exhaust port 107a is formed as a through hole in the exhaust port member 107 for connecting the output chamber 102 and the exhaust chamber 103.
The poppet valve 108 is structured from a shaft portion (stem) 108a that is inserted into and supported in the supply air port 106a output chamber, an umbrella-shaped valve unit (first valve unit) 108b for opening and closing the opening portion 106a1, facing the input chamber 101 side of the supply air port 106a, formed on one end of the shaft portion 108a, and a valve unit (second valve unit) 108c for opening and closing an opening portion 107a1, facing the output chamber 102 side of the exhaust port 107a, formed on the other end of the shaft portion 108a. 
The first valve unit 108b of the poppet valve 108 is biased toward the output chamber 102 side by a poppet valve spring 109, and a first ON/OFF valve 110 is structured from the first valve unit 108b and the supply air port 106a, and a second ON/OFF valve 111 is structured from the second valve unit 108c and the exhaust port 107a. 
In this pressure-reducing valve 100, the diaphragm 105 is biased toward the output chamber 102 by a pressure-regulating spring 112, where the degree of biasing of the diaphragm 105 by the pressure-regulating spring 112 is adjusted by a pressure-regulating knob 113, to set the pressure of the pressurized fluid that is outputted from the output chamber 102. This pressure that is set is termed the “setpoint pressure.”
The diaphragm 105 is positioned so that, when pressed against the output chamber 102 side, the center of the exhaust port 107a matches the shaft line of the poppet valve 108 (the axis of the shaft portion 108a), so that the opening portion 107a1 of the exhaust port 107a is covered by the second valve unit 108c of the poppet valve 108.
When the diaphragm 105 is biased toward the output chamber 102, the second valve unit 108c of the poppet valve 108 closes the opening portion 107a1 on the output chamber 102 side of the exhaust port 107a, and is pushed against the exhaust port member 107 so that the shaft portion 108a of the poppet valve 108 moves toward the input chamber 101, so that the first valve unit 108b of the poppet valve 108 moves away from the opening portion 106a1 of the supply air port 106a. 
In this state, that is, in a state wherein the first ON/OFF valve 110 is open and the second ON/OFF valve 111 is closed, when the pressurized fluid from the outside is inputted into the input chamber 101 through the input flow path 114, the inputted pressurized fluid enters into the output chamber 102 through the supply air port 106a, and is outputted to the outside through an output flow path 115.
In this state, when the output pressure POUT rises above the setpoint pressure, the diaphragm 105 moves toward the exhaust chamber 103. Given this, the second valve unit 108c of the poppet valve 108, which is biased toward the opening portion 107a1 of the exhaust port 107a also undergoes movement toward the exhaust chamber 103, where the movement of the shaft portion 108a of the poppet valve 108 accompanying this movement causes the first valve unit 108a of the poppet valve 108 to close the opening portion 106a1 of the supply air port 106a. 
When the diaphragm 105 moves further toward the exhaust chamber 103, the second valve unit 108c of the poppet valve 108 moves away from the opening portion 107a1 of the exhaust port 107a. When this state is produced, that is, when the first ON/OFF valve 110 is closed and the second ON/OFF valve 111 is opened, the pressurized fluid within the output chamber 102 passes through the exhaust port 107a to enter into the exhaust chamber 103, and then is discharged to the outside of the pressure-reducing valve 100 through the exhaust hole 116.
Through this, the pressurized fluid within the output chamber 102 is decompressed, so that the diaphragm 105 is biased toward the output chamber 102, to close the second ON/OFF valve 111. This operation is repeated to achieve regulation of pressure within the output chamber 102, resulting in a pressurized fluid that has been decompressed to the setpoint pressure being outputted to the outside from the output chamber 102 through the output flow path 115.
However, in such a pressure-reduced valve 100, it is difficult to completely cut off the fluid using the second ON/OFF valve 111, and thus there is leakage (bleeding) of pressurized fluid to the outside from second ON/OFF valve 111. Because the bleeding is no more than a release of fluid to the outside, preferably there is as little bleeding as possible. That is, the bleeding from the pressure-reducing valve 100 can be considered to be wasteful of the fluid that is being handled, and a reduction thereof contributes directly to improved environmental friendliness in terms of resource conservation and energy conservation.
Given this, in this pressure-reducing valve 100, the structure is so as to minimize, insofar as is possible, the bleed flow rate, where the bleed flow rate is the leakage of the pressurized fluid to the outside from the second ON/OFF valve 111. This point will be explained in detail below.
In the pressure-reducing valve 100 illustrated in FIG. 7, the diaphragm 105, as illustrated in FIG. 8, must be disposed facing the opening portion 107a1 of the exhaust port 107a and the second valve unit 108c of the poppet valve 108, so that the opening portion 107a1 of the exhaust port 107a will be blocked by the second valve unit 108c of the poppet valve 108 when the diaphragm 105 moves toward the output chamber 102 side. More specifically, when the pressure-reducing valve 100 is assembled, the diaphragm 105 is positioned so that the center of the exhaust port 107a is aligned with the shaft axis of the poppet valve 108.
In the state illustrated in FIG. 8, the main pressure-regulating mechanism is assembled so as to be coaxial, that is, is assembled so that the centerline of the exhaust port 107a and the shaft axis of the poppet valve 108 are coaxial, in the ideal state wherein the bleed flow rate is extremely low. However, this state is difficult to achieve.
That is, because the diaphragm 105 is made from material that has flexibility, the tolerance is large, and thus positioning so that the center of the exhaust port 107a is aligned with the shaft axis of the poppet valve 108 at first in assembly is difficult. Moreover, even if this positioning were possible, the diaphragm 105 is stretched in the process for screwing down the peripheral edges thereof, producing non-uniformities, causing the position to shift.
The variability of the shift in this position appears, as-is, in variability in the bleed flow rate, and thus an upper limit is placed on this variability in the product specification. In practice, assembly on the manufacturing work floor is usually carried out while making fine adjustments in order to reduce the variability to be less than the specification value required for competitiveness in the market. Of course, this requires skill in making adjustments during assembly, and has a negative effect on operating efficiency. Moreover, this also has a negative effect on ease of maintenance in the field.
Note that in the pressure-reducing valve 100 illustrated in FIG. 7, the peripheral edge portion 107b of the opening portion 107a1 of the exhaust port 107a, as illustrated in FIG. 8, is conical, and the tip end of the second valve unit 108c of the poppet valve 108 is hemispherical, so that the tip end of the second valve unit 108c presses against the peripheral edge portion 107b of the opening portion 107a1 of the exhaust port 107a to center the center of the exhaust port 107a on the shaft axis of the poppet valve 108.
That is, as indicated in FIG. 9, with the center of the exhaust port 107a prior to centering indicated by J1, the tip end of the second valve unit 108c is pressed against the peripheral edge portion 107b of the opening portion 107a1 of the exhaust port 107a and the diaphragm 105 is pulled and the tip end of the second valve unit 108c enters into the center of the peripheral edge portion 107b of the opening portion 107a1 so that the center J1 of the exhaust port 107a, prior to centering, will be aligned with the center of J0 of the second valve unit 108c of the poppet valve 108.
However, when this structure is used, the position of the exhaust port 107a in the crosswise direction is constrained by the poppet valve 108, and when the center of the diaphragm 105 is shifted or there is a large deformation strain, then the sliding friction of the guiding portion that guides the sliding of the poppet valve 108 will be large. Note that while in some cases there is a guiding structure between the poppet valve and the exhaust port (referencing, for example, Japanese Unexamined Utility Model Registration Application Publication No. H5-40668, Japanese Unexamined Patent Application Publication No. H11-311349, and Japanese Unexamined Patent Application Publication No. 2007-218424), the same is true in these structures as well, where the sliding friction of the guiding portion will be large.
When the sliding friction of the guiding portion is large, then, from the perspective of controllability, there will be hysteresis and lag time in control operations of the pressure-reducing valve, and when a precision high-speed response instrument is connected to the output side, this has a negative impact on the controllability of the instrument that is connected.
The present invention solves the problems set forth above, and the object thereof is to provide a pressure-reducing valve requiring no skill in adjusting at the time of assembly, wherein it is possible to improve operating efficiency and field maintainability, and wherein essentially no sliding friction is produced even when there is a large offset in the centering of the diaphragm and a large deformation strain.